It is well known that the partial pressure of oxygen in the atmosphere decreases with altitude. For this reason it is necessary to provide the pilot and crew of high altitude aircraft with breathing systems in order to prevent hypoxia at high altitudes. Some of the breathing systems involve the use of auxiliary oxygen systems onboard the aircraft. At certain altitudes, the cabin pressurization system may malfunction leading to cabin depressurization. In the event of this occurrence, aircraft flying at high altitudes require auxiliary oxygen systems to provide oxygen to passengers and crew. In these auxiliary oxygen systems, oxygen is provided to the pilot and crew by oxygen masks worn on their faces that are supplied from an oxygen source through a pressure step-down regulator. The auxiliary oxygen supply system typically has multiple flowlines, some of which pass through areas of the aircraft fuselage that are at higher risk of damage due to engine failure (which might send broken pieces through said supply lines). It is important to have a mechanism that will automatically stop oxygen flow in such cases in order to avoid wasting the oxygen supply and feeding potential fires, to continue flow to operating lines and to avoid potential O2 buildup in pre-compromised areas of the craft.
Such a system comprised of an oxygen source, a central-oxygen pressure step-down regulator, a flow control means, and an emergency shut-off mechanism attached in a low-risk area of the craft to each of a multiple of oxygen distribution lines. In these breathing systems it is possible that a riser line carrying oxygen may become severed during flight. It is desirable that the flow of oxygen cease flowing through the compromised line, while oxygen continues to flow at a specified rate through the non-compromised line. It is also desirable that the pressure based on the altitude of the aircraft.
Most or all of the oxygen systems used presently on operational aircraft lack a mechanism to disable the flow of oxygen to the masks in the event that an oxygen line becomes severed. The systems known in the art generally comprise a plurality of oxygen generators, or tanks, a regulator to control the flow of oxygen and means for connecting to a mask. If an oxygen line is severed, oxygen will continue to flow through that line, never reaching the masks. This leads to the excessive depletion of stored oxygen supplies, which is both wasteful and unsafe. While breathing systems are known to employ valves that regulate flow based on altitude, these valves will not shut off when a line is severed. While the prior art oxygen systems themselves are adequate, the problem can be corrected by technological advances in the valve technology that is used in conjunction with these systems.
Prior art valves, such as simple ball and check valves, have a number of problems associated with them when utilized in auxiliary oxygen systems. The valves only operate between extremes and are either completely open to allow full flow, or completely closed to prohibit flow. These valves have no provisions to accommodate the varying functions of the flow regulator. Other prior art valves, are simply flow control devices, and do an adequate job of regulating flow, however they can not serve as shut-off valves should an emergency condition arise, such as the severing of an oxygen line. Furthermore, prior art shut off valves react instantaneously to changes of pressure, closing the valve as a result of transient pressure variations.
Additionally, prior art shut off valves are highly erratic and tend to inadvertently close during normal operation. It is also desirable for this valve to have a time delay.